Research On The Switching Property And Polarization Characteristics Of Nonlinear Optical Loop Mirror

The study of fiber laser is a very important area in the nonlinear opticalresearch, which is regarded as one of the key technologies for the generationof high performance ultra-short optical pulse needed for the modern longdistance, ultra-high bit rate optical communication systems. Nonlinear OpticalLoop Mirror (NOLM) is a new type of fiber device which is used in manyoptical fields, such as optical switch, wavelength conversion, wavelengthdivision multiplexing, optical fiber laser, etc. In recent years, nonlinearoptical loop mirror constructed with dispersion decreasing fiber which isemployed to pulse compress and pedestal suppression is research widely, andthe polarization characteristics of the pulse propagating in the nonlinearoptical loop mirror is also researched widely.In this dissertation, the performance of a nonlinear optical loop mirrorcomposed of a dispersion decreasing fiber (NOLM-DDF) is investigatednumerically. The switching characteristics and the pulse compression effect ofthe NOLM-DDF is simulated. Results show that ultroshort pedestaless pulsecan also be generated when an asymmetric coupler is adopt, with shorter fiberneeded. When proper coupler ratio is chosen, output pulse with little pedestalcan be generated, the performance of soliton evolution in the highbirefringence fiber and the infection of the nonlinear birefringence to theswitching characteristics and pulse propagation characteristics are alsoinvestigated numerically.This dissertation consists five chapters:Chapter 1: introduce the basic structures of NOLM, presents theapplications and the research evolutional history of the NOLM.Chapter 2: theoretic elements of the NOLM. At the basis of Maxwellequations, using the confined condition of optical fiber waveguide, Analyzes the mechanisms of the NOLM, including the propagation equations of opticalpulse in fibers and the mechanism of optical coupler and the optical switch.Chapter 3: Propagation characteristics of hi-order pulse in a nonlinearoptical loop mirror constructed from a dispersion decreasing fiber, theperformance of a nonlinear optical loop mirror composed of a dispersiondecreasing fiber (NOLM-DDF) is investigated numerically. The switchingcharacteristics and the pulse compression effect of the NOLM-DDF issimulated. Results show that ultroshort pedestaless pulse can also be generatedwhen an asymmetric coupler is adopted, with shorter fiber needed. Whenproper coupler ratio is chosen, output pulse with little pedestal can begenerated. The conclusion has significance in choosing parameters underexperimental practice.Chapter 4: The infection of linear birefringence and nonlinearbirefringence in nonlinear optical loop mirror. In this chapter, the stability ofoptical soliton in the birefringence fiber is researched, the pulse propagatingcharacteristics and switching characteristics of NOLM constructed fromhigh-birefringence fiber are analyzing numerically, and the stochasticbirefringence effect in the NOLM is also investigated.Chapter 5: summing-up of the dissertation. Summarize the essence of thedissertation, and raise some points and problems of future research.